The power amplifier circuit is important to a radio frequency emitter circuit. The power amplifier circuit is usually configured at the front-end circuit of an RF transmitter for amplifying and then outputting a signal. The power amplifier circuit is the most power consuming circuit at the front-end circuit of the RF transmitter, and is widely used in broadband electronic devices and equipment, such as mobile phones, tablets, satellite communication devices or the like. Among these applications, the power amplifier circuit is essential for mobile phones.
However, the linearity of the power amplifier circuit can be bad especially when its output power gets large, because the gain of the power amplifier circuit will drop gradually with an increase of its output power when the amplifier circuit gets saturated. This often happens to a multi-stage amplifier circuit.